It isn't exactly perfect in terms of starting time, but it will nontheless correctly fully activate in some time. Has built in overflow protection. Buffer limits are set at exacly 40 U-235 to 1 cenrifuge as I like to keep as fewer unused uranium as possible. You can change it to as many as you want (double the desired amount by 2 and set in the combinator)
IMPORTANT: For first start DO NOT put the existing U-235 directly into cenrifuges!!!
Feed it to the start of the output belt line with yellow inserter set to 1 item per swing.